Rolling mill motor speed control apparatus



Oct. 26, 1965 J. w. COOK ROLLING MILL MOTOR SPEED CONTROL APPARATUS 4Sheets-Sheet 1 Filed Jan. 31, 1965 Oct. 26,

Filed Jan J. W. COOK 4 Sheets-Sheet 2 scREwDowN /26 scREwDowN '3 eo Q 24l /loo /liz l 28 AMPLIFIER .'/26 AMPLIFIER @D30 9 (Wl [L /l24 SPEEDSPEED REGULATOR REGULATOR THREAD BUS RUN BUS lNvENToR John W. Cook BYL/AT'ToRNEwr Oct. 26, 1965 J. w. COOK ROLLING MILL MOTOR SPEED CONTROLAPPARATUS Filed Jan. 5l, 1965 4 Sheets-Sheet 5 m. .32 s mmm ...mmm QmmamSTAND Fig. 3

RUN SPEED THREAD SPEED TIME Fig. 5

Oct. 26, 1965 J. w. cooK 3,213,656

ROLLING MILL MOTOR SPEED CONTROL APPARATUS United States Patent O3,213,656 ROLLING MILL MTR SPEED CQNTRL APPARATUS .lohn W. Cook,Monroeville, Pa., assigner to Westinghouse Electric Corporation,Pittsburgh, Pa., a corporation of Pennsylvania Filed dan. 31, 1963, Ser.No. 255,269 Claims. (Cl. 72-15) The present invention relates in generalto motor speed control apparatus and more particularly to motor Speedcontrol apparatus for varying the operative speed of one or more drivemotors of a workpiece rolling mill such as the finishing train of a hotstrip mill for steel rolling.

In the well known operation of a hot rolling mill having at least onedrive' motor, up to the present time, all of the stands of the rollingmill had been threaded at running speeds up to two thousand feet perminute. The workpiece slabs have in the past been of such size thatdelivered strips about two thousand feet in length have requiredapproximately sixty seconds of elapsed rolling time.

It has recently been contemplated to increase the incoming slab weightsto obtain larger and longer coils of rolled strip without the necessityof providing welds between delivered strip portions. It a four thousandfoot long strip is delivered from a rolling mill operating in the orderof two thousand feet per minute, this would require about two minutes oftime to complete the rolling operation. Such an elapsed time results inundesired temperature losses particularly, in the tail-end of the stripas compared to the leading-end of the strip. A higher rolling mill speedcould reduce this elapsed rolling time but this presents threadingproblems for both the rolling mill and the subsequent coil windingequipment for winding the rolled strip into a coil.

Accordingly, it is an object of this invention to provide an improvedmotor speed control apparatus for the drive motors of a rolling millsuch that a more suitable workpiece threading speed is provided and amore rapid acceleration of the rolling mill to a higher and desiredrunning speed is effected to result in a better operation of the rollingmill and to increase the productivity of the rolling mill.

It is a different object to provide an improved motor speed controlapparatus for the motors operative with a strip rolling mill such thatundesired temperature effects are minimized relative to the rolling ofany particular workpiece strip and permitting the rolling of stripshaving a greater length than was previously practical and in additionsuccessive workpiece strips can be passed through the rolling mill withless time required between the respective rolling schedules.

In accordance with the teachings of the present invention, a speedcontrol apparatus for a tandem type hot strip mill drive system isprovided to be operative under a first threading speed and thenaccelerated to a higher running speed. Two, speed reference buses areprovided for this purpose. One is the thread-speed bus and the other isthe run-speed bus. The thread-speed bus is supplied by a separate,thread-exciter generator which controls the voltage of the thread-speedbus. The runspeed bus is energized by a combination of the samethread-exciter generator plus a run-exciter generator which areconnected together such that the run-speed bus voltage is the sum of theoutput voltages of the two exciter generatorS. The thread-bus voltage isset by an adjustable reference working in the thread-exciter generatorvoltage regulator and the run-bus voltage is controlled at a maximumvalue by a voltage limiting device operative with a ramp functiongenerator connected to control the output voltage of the run-excitergenerator. The desired flexibility of operation is provided andprotection against operation of the drive motors in excess' of ratedyspeed is provided.

These and other objects and advantages of the present invention willbecome apparent in view ot the following description taken inconjunction with the drawings wherein:

FIGURE l is a diagrammatic showing of the control apparatus inaccordance with the present invention;

FIGURE 2 is a schematic showing of the present control apparatusoperative with two stands of a multiple stand rolling mill;

FIG. 3 is a graph showing the well known speed cone or relativeoperative speeds for the multiple stands of the rolling mill;

FIG. 4 is a schematic showing of the speed control apparatus for thestrip winding apparatus in accordance with the present invention; and

FIG. 5 is a graph showing the speed changes effected by this controlapparatus.

In FIGURE l there are shown six stands of the finishing train for a hotstrip mill with the strip entering successively a first stand 10, asecond stand i2, a third stand 14, a fourth stand 16, a fifth stand 18and a sixth stand 2li from which it passes across a roll table 22 to astrip winding device 24.

Each of the stands is provided with a screwdown mechanism, such as thescrewdown mechanism 26 operative with the first stand 10. Similarly,each of these stands includes a drive motor, such as the drive motor 28operative with the first stand 10. Each of the drive motors iscontrolled in speed by the output voltage from a generator operativewith the armature ot the drive motor. For the first stand 10 thisvoltage is provided by a stand generator 3i) shown operative with thedrive motor 28. A speed regulator for each stand is provided to energizethe field of the generator, such as the speed regulator 32 provided forthe first stand 10 and operative with the field winding 34 of thegenerator 30.

There are provided a thread-voltage bus 40 and a runvoltage bus 42,operative with each of the rolling mill stands. The thread-bus 4i) isenergized by a thread voltage exciter generator 44 connected between acommon return conductor 46 and the thread voltage bus 4i). A run voltageexciter generator 48 is connected between the common-bus 46 and therun-voltage bus 42 in series with the thread voltage exciter generator44, such that the output voltage from the run exciter 48 is added to theoutput voltage from the thread exciter generator 44 and provided betweenthe run-voltage bus 42 and the common conductor 46.

The speed regulator for each stand includes a voltage sensing impedancemember operative with a first contactor connected between the commonconductor 46 and the thread-bus 4i) and a second contactor to connectthis impedance member between the common conductor 46 and the run-bus42. More specifically, the first stand speed regulator 32 operative withthe first stand 1i) includes a voltage sensing impedance member Si)operative with a first contactor 52, which when closed connects theimpedance member 5i) between the thread-bus 40 and the common conductor46 such that the movable tap 54 provided with the impedance member Silis adjustable to provide a predetermined and desired speed range for themotor 28 of the first stand Titi and is connected to energize the speedregulator 32 through a vernier resistor 56. A second contactor 58 isoperative to energize the resistor 50 between the run-bus 42 and thecommon conductor 46.

A roll force sensing device 62 is operative with the first stand forproviding an output signal to indicate the roll force loading of thefirst stand or when the workpiece strip 60 is passing through the rststand 10. A similar roll force loading sensing device is provided foreach of the stands of the rolling mill, with each of the respective rollforce sensing devices being connected to a sequence control apparatus 64operative to open and close the respective contactors for each of thestands, such as the contactors 52 and 58 operative with the first stand10 as will be later described.

The strip winding device 24 is provided with a drive motor 70 and amotor load sensing device 72 operative to sense the loading of the stripwinding device 24 through the armature current of the motor 70. Ifdesired a suitable sensing member may be provided such as a tensionmember operative with the strip entering the winding device to indicatewhen the winding device 24 is applying tension to the workpiece strip60.

A first ramp signal providing generator 80 is operative with a fieldwinding 82 of the thread exciter generator 44 for providing the desiredramp function pattern to the energization of the thread-bus 4t) relativeto the common conductor 46. A run ramp signal providing generator 84 isoperative with a field Winding 86 of the run exciter generator 48 forcausing the voltage of the run-bus 42 to increase above the threadvoltage of the thread-bus 40 in a ramp function pattern. This is doneafter closing the run contactors, such as the contact 58 for the firststand is closed, and after opening the thread contactors, such as thecontactor 52 for the first stand 10, by the sequence control apparatus64.

In FIG. 2 there is schematically shown a portion of the controlapparatus of the present invention operative to sequence the opening andclosing of the respective contactors to switch the operation of thestand drive motors from the thread-bus 40 to energization by the run-bus42. In FIG. 2 there is shown the output signal from the roll forcesensing device 62 being applied to a signal arnplifier 100 responsive toa minimum roll force signal to control the operation of a contactor 102connected through a time delay 104 to energize the control winding 106operative with the contactor 52. The contactor 102 also controls theenergization of the control winding 108 operative with the contactor 58.The sixth stand is shown including a roll force sensing device 110providing an output signal through a minimum signal responsive amplifier112 to energize a control winding 114 operative with a contactor 116which controls the energization from a suitable voltage source 118 of acontrol winding 120 through a time delay device 122, which controlwinding 120 is operative with a contactor 122 connected between thespeed regulator 124 for the drive motor 126 of the sixth stand 20 andthe thread-bus 40. The contactor 116 also controls the energization of acontrol winding 128 operative with a contactor 130 connected between therunebus 42 :and the speed regulator 124 for the drive motor 126. Itshould be understood in this regard that the stands 12, 14, 16 and 18are similarly provided with control circuitry such as shown for stands10 and 20.

The strip winding device 24 is provided with a motor load sensing device72 which energizes a control winding 140 operative with a contactor 142connected between the voltage source 118 and the respective controlwindings for each of the contactors connected between the thread-bus 40and the run-bus 42 and the respective speed regulators for all of thestands 10, 12, 14, 16, 18 and 20.

In FIG. 3 there -is shown a curve illustrating the speed cone for therespective stands of the rolling mill shown in FIG. l. The curve of FIG.3 is plotted in terms of speed in feet per minute of the respectivestands as a function of the stands. As illustrated in FIG. 3, forpurpose of example only, the first stand 10 may be operative between aspeed range of 300 feet per minute and 70() feet per minute. The secondstand may be operative between a speed of 450 feet per minute and 1200feet per minute. The third stand 14 may be operative between a speed of700 feet per minute and a speed of 1750 feet per minute.

The fourth stand 16 may be operative between a speed of 900 feet perminute and a speed of 2250 feet per minute. The fifth stand 18 may beoperative between a speed of 1300 feet per minute and 3200 feet perminute. The sixth stand 20 may be operative between a speed of 1500 feetper minute and 3750 feet per minute. It should be understood that thecurve shown in FIG. 3 is for purpose of illustration only and anydesired changes or variations in the relative speed ranges of therespective stands could be made in accordance with the present knowledgeand skill of the rolling mill art.

In FIG. 4 there is shown an application of the present control apparatusfor controlling the operative speed of the motor 70 of the strip windingdevice 24 through energization first by the thread-bus 40 andsubsequently by the run-bus 42. As the workpiece strip 60 enters thestrip winding device 24, it is desired to sense the resultant additionalloading of the motor 70 to energize the control winding and close thecontactor 142, such that the regulator operative to energize a fieldwinding 152 of the generator 154 operative with the strip winding devicemotor 70 will change the operative speed of the strip winding device 24from a threading speed as determined by the voltage of the thread-bus 40to a run-speed as determined by the voltage of the run-bus 42. It shouldbe understood that a current of tension regulator can be operative withthe generator 154 and a counter E.M.F. regulator with the field windingof the motor 70, such that the counter regulator reference is heldproportional to strip speed to provide a substantially constant striptension. The closing of contactor 142 energizes a control winding 156 toopen contactor 157 through a time delay device 158 and energizes acontrol winding 160 to close a contact member 162. Thusly, when the loadsensing device 72 indicates that a strip has entered the strip windingdevice 24, the contactor 142 is closed resulting in closing of thecontactor 162 and subsequently as determined by the time delay 158 theopening of the contactor 157 to change the energization of the speedregulator 150 from across the thread-bus 40 relative to the commonconductor 46 and instead to be energized by the run-bus 42 relative tothe common conductor 46. Thusly, as the voltage of the run-bus 42 isincreased in a ramp or linear function such as shown in FIGURE 5 by theramp generator 84, the operative speed of the motor 70 is in this mannercaused to increase from the predetermined thread-speed to the desiredand predetermined run-speed. The respective predetermined speeds are setby the maximum output voltages provided by the thread and the runexciter generators when the top of the ramp control signals are suppliedto the respective generator field windings for those generators.

In FIGURE 5 there is shown a curve to illustrate the ramp functionchange of the thread signal to a .predetermined maximum value 200 toprovide the desired thread speed pattern and the subsequent rampfunction increase to a predetermined maximum value 201 to provide thedesired operative run-speed pattern for the rolling mill. Eachindividual stand has a particularly desired operative speed inaccordance with the curve shown in FIG- URE 3, with all of the standsbeing controlled to follow the thread-speed and run-speed pattern shownin FIG- URE 5.

In the operation of the control apparatus `shown in FIG. l the threadcontactor for each of the stands 10, 12, 14, 16, 18 and 20, andcorresponding to the contact member 52 shown for stand 10, is normallyclosed to energize the speed regulator and thereby the stand generatorto control the operation of the stand drive motor such that the firststand 10 and the other stands operate `at a thread-speed determined bythe voltage of the threadbus 40 from the excitation generator 44. Inthis regard, it should be understood that the thread ramp generator 80initially controlled the operation of the exciter generator 44 throughthe generator field 82 such that the voltage of the thread-bus 40 wascaused to increase initially in a ramp function or linear manner to apredetermined maximum or thread run excitation voltage. This is shown bythe curve of FlGURE 5. When the workpiece strip 60 has passed througheach of the stands 10, 12, 14, 16, 18 and 20 land passes the run-outtable rollers 22 and enters the strip winding device 24, this changesthe loading of the drive motor 7 0 operative with the strip windingdevice 24 such that the motor load sensing device 72 can provide anoutput signal to a sequence control apparatus 64. This causes thecontactors connected between the run-bus 42 and the respective speedregulators for the stand drive motors to close and subsequently to openafter a provided time delay the normally closed contactors connectedbetween the thread-bus 40 and the speed regulators for the respectivestands. In this regard, it should be noted that a voltage sensing device45 is operative with the run-bus exciter generator 48 and provides anoutput control signal to the sequence control apparatus 64 such thatonly when the output voltage of the run exciter generator 48 is zero canthe normally open contactors operative with run-bus 42, such as thecontactor 58, be closed. When the control signal from the load sensingdevice is provided to the sequence control apparatus to indicate thatthe workpiece strip 60 has entered the strip winding device 24, it isnow desired to increase the operating speed of each of the stands 10,12, 14, 16, 18 and 20 as well as to increase the operating speed of thestrip winding device 24 from the thread-speed to the higher desiredrun-speed. To do this, the sequence control apparatus 64 closes thecontactors connected between the run-bus 42 and each of the speedregulators for the respective stand motors. After a suitable time delay,the contactors open which are connected between the thread-bus 40 andthe stand speed regulators. Now the run ramp generator 84 begins toincrease the output voltage from the excitation generator 43 such thatthe operating speed of the drive motors for each of the respectivestands is increased to a predetermined maximum running speed establishedby the adjustment potentiometer.

Thusly, as shown in FIG. 5, a typical stand will initially acceleratefrom a zero speed to a desired thread speed 200. When the workpiecestrip 60 enters the strip winding device 24, the speed of thatindividual stand will increase in a ramp function or linear manner to adesired run speed 201 as determined by the maximum voltage energizationof the run-bus 42. After the workpiece 60 passes through that particularstand, the operative speed `of the stand will then decrease in apredetermined manner by dynamic braking or the like back to thethread-speed 200 and it will remain at the threadspeed until a secondworkpiece strip has been threaded through all of the stands of therolling mill and enters the strip winding device at which time theoperative speed of that particular stand will again increase in a rampfunction manner to the desired run speed 201.

As shown in FIGURE 1, each stand includes a roll force sensing device,such as the roll force sensing device 62 provided for the first stand10. This provides an output signal to the sequence control apparatus 64which causes the operating speed of that particular vstand to decreasefrom the run-speed 201 shown in FIGURE 5 back to the thread-speed 200when the workpiece strip 60 has passed through that particular stand. Inother words, when the workpiece strip 60 leaves, the operating speed ofthe lirst stand will change from the run-speed back to the thread-speed.Subsequently, as the tail end `of the workpiece strip passes through thesecond stand 12, it will then change from run-speed to thread-speed.This speed changing operation will successively move through theplurality of stands in conjunction with the tail-end of the workpiecestrip 60 passing through the respective stands. rThis allows asucceeding workpiece strip to enter stand 10, for example, before thetail-end of the preced- 6 ing workpiece strip 60 has left stand 20. Intheory, depending upon the time .period required to decelerate the firststand 10 from its run-speed to its thread-speed, the leading end of thesucceeding workpiece strip could enter stand 10 before the tail-end ofthe preceding workpiece strip traveling at run-speed had left the secondstand 12.

As shown in FIG. 2, the strip winding device 24 is provided with a motorload sensing device 72 to close the contactor 142 when the workpiecestrip enters the strip winding device 24 which energizes the controlwinding 108 for the normally open contactor 58 and the correspondingcontrol winding 128 for the normally open contactor 130, for therespective first stand 10 and last stand 20 of the rolling mill, fromthe voltage source 11S whenever the workpiece strip 60 enters the stripwinding device 24. This simultaneously changes the operating speed ofeach of the stand drive motors from the thread-speed to the run-speed inaccordance with the ramp function or linear increase in the voltageenergization of the run-bus 42. On the other hand, the roll forcesensing device 62 operative with the tirst stand 10 individually opensthe normally closed contactor 102 operative only with the irst standspeed regulator 32 when the workpiece strip 60 leaves the irst stand 10.When contactor 102 opens, this opens the normally open contactor 5S andcloses the normally closed contactor 52 to cause the speed regulator 32to change the operative speed of the drive mot-or 28 for the rst stand10 from its run-speed to its thread-speed as shown in FIG. 5. As thetrailing end of the workpiece ystrip passes through the rolling mill andeventually passes through the sixth stand 20, the roll force sensingdevice similarly opens the normally closed contactor 116 to result inopening of the normally open contactor member and closing the normallyclosed contactor 122 to cause the speed regulator 124 for the drivemotor 126 of the sixth stand 20 to change its operating speed from therun-speed to the threadspeed as shown in FIG. 5.

The apparatus shown in FIG. 4 is similarly operative to sense theincreased load taken by the motor 70 when the workpiece strip 60 enterslthe strip winding device 24. This closes the normally open contactor142 to result in closing the normally open contactor 162 and to open thenormally closed contactor 157. This causes the tension regulator toenergize the drive motor 70 through the generator 154 in accordance withthe increased voltage of the run-bus 42 as compared to the previousthread-bus 40 energization of the tension regulator 150.

Thusly, it will be seen that when the tail-end of the workpiece strip 60drops out of any particular stand of the rolling mill, that stand isreset to its thread-speed to be ready to accept the head-end of the nextworkpiece strip or bar t-o enter the rolling mill. This avoids thenecessity of waiting until the tail-end :of a particular workpiece stripleaves the last stand of the whole rolling mill to then reset the entirerolling mill in a single operation to the thread-speed. In accordancewith the teachings of the present invention, the successive workpiecestrips are permitted thereby to enter the rolling mill on a morefrequent time schedule and are closer together such that only a fewseconds is required between the tail-end of a previous workpiece stripto leave a particular stand of the rolling mill and the entry of thehead-end of the next and succeeding workpiece strip.

The two reference exciter generators 44 and 48 as shown in FIG. 1 areprovided to supply the desired speed reference signals to the standspeed regulators. The threadbus 40 is operative as 'a reference bus toset the threadspeed of the whole rolling mill. This reference threadbus40 is regulated and adjustable over a nominal range of approximately1,500 feet per minute to approximately 2,500 feet per minute. The runexciter generator 48 then supplies the additional required excitationvoltage which is added directly to the output voltage of the threadexciter generator 44 such that the run-speed is set bythe sum or" thethread exciter output voltage and the output voltage from the runexciter generator 48. The voltage output of the generator 48 is adjustedby the speed operator to allow setting the running speed of the rollingmill in accordance with any desired work schedule. This in theory couldvary over a range from the thread-speed operation to a valuecorresponding to the top speed of the rolling mill. The stand speedsetting motor operated rheostat, such as the rheostat 50 for the stand10 and the Vernier rheostat 56 are used to set the individual standspeeds for the various rolling schedules substantially in accordancewith the conventional practice at the present time and the curve shownin FIGURE 3. The speed regulator, such as the speed regulator 32`operative with the first stand 10, is operative with either the eldwinding of the drive motor or could be operative with the power supplyconnected to energize the motor armature.

In a typical operation, the mill operator will set the thread-speed forthe mill to `a value which he knows to be correct by setting the threadexciter output voltage from the exciter generator 44. In addition, themotor operated rheostat 51 of the last stand 20 is set to provide thedesired speed operation for the last stand 20. The other stands will beset to their correct speed by operation of the individual stand motoroperated rheostat. The operator will then set the top run-speed byadjusting a potentiometer S3 operative with the run ramp generator 84 todetermine the maximum output voltage of the run exciter generator 48.However, the run exciter generator 48 will have a zero output voltageuntil it is properly sequenced to go to the increased output voltagevalue and which zero output voltage i-s provided when the sequencecontrol apparatus 64 operates to close the run contactors correspondingto the contactor 58 operative with the first stand 10. A workpiece strip60 is then threaded into the rolling mill at the set thread-speed. Assoon as the headend of the workpiece strip 60 enters the down coiler orstrip winding device 24, the mill acceleration will be initiated by themotor load sensing device 72. The run exciter generator 48 will thenincrease its output voltage in a ramp function buildup manner to apredetermined top speed value. The desired ramp function pattern can becontrolled by any of the well known ramp function generator devices suchlas a motor operated rheostat or the like. The whole of the rolling millwill then accelerate from the threading-speed toward the running-speedin conjunction with the voltage increase of the run-bus 42.

When the tail-end of the workpiece strip leaves stand 10, the roll forcesensing device 62 which could if desired be a Well known load relay orsome other sensing device, will cause the contactor 58 to open and thecontactor 52 to close. Stand 1 will then be decelerated back tothread-speed. In a similar manner, when the tail end of the workpiecestrip leaves stand 12, the illustrated control apparatus will causestand 12 to be reset to threadspeed. All other stands follow thispattern of operation in -a similar manner. When the tail end of thestrip enters the winding device 24 the run reference exciter generator48 will be returned to a zero output voltage value and all the contactsoperative with the thread-bus 40 will then be closed and the contactscorresponding to contact 58 operative with the run-bus 42 will be open.The mill control apparatus will then be ready to accelerate the rollingmill from the thread-speed to the run-speed when a new workpiece striphas been threaded through the six stands of the rolling mill and hasentered the strip winding device 24.

The operation of the present control apparatus is such that the head-endof a succeeding workpiece rstrip may actually have entered the iirststand or iirst few stands of the rolling mill before `the tail-end ofthe preceding Workpiece strip has passed through the final stand 20. Thepractical limitation controlling the spacing between the successiveworkpieces is -how long it will take before the individual stand motorscan be reset from their run-speed to the lower thread-speed.

The contactor for each stand corresponding to contactor 52 should remainclosed for a short time after the contactor 5S for each of the stands isclosed. Further the latter contactor 58 can close only at zero voltageoutput from the run exciter generator 48. Similarly it is mandatory whenchanging from the run-speed operation for a given stand to thethread-speed operation, that the contactor 58 open before the contactor52 is closed. The roll force sensing device 62 for a particular standsuch as stand 10 will initiate the opening of the contactor 58 when theworkpiece leaves that stand. When the headend of the workpiece stripenters the strip Winding device 24, this will initiate the closing ofthe contactor 58 when it is desired to change to the higher run-speed.

It should be further noted that the last stand motor operated rheostat51 will be c-alibrated in feet per minute at top desired mill speed. Inother words, if the speed range of the last stand 20 is between 1,30()feet per minute and 3,750 feet per minute at rated output voltage fromthe run exciter generator 48, the preset rheostat 51 will be calibratedfrom 1,300 to 3,750 feet per minute. In addition, the energization ofthe run-bus 42 will be such that regardless of the actual operatingspeed of the rolling mill, the run-bus 42 will always go to the samevoltage level during the normal run condition. The run excitationprovided by the run-bus 42 is the sum of the output voltages provided bythe thread exciter generator 44 and the run exciter generator 48. Itshould be further understood that further adjustment of the thread speedmay be provided by an additional control eld winding for the threadexciter generator 44 to determine the actual output voltage supplied bythe thread exciter generator 44 to the thread bus 40. The voltagesensing device 45 only allows the sequence control apparatus 64 to closethe run-bus contactor 58 when the output voltage supplied by the runexciter generator 48 per se, is zero. The voltage limit circuit 47 isoperative to limit the reference voltage of the run bus 42 to itscorrect desired maximum value. The operation of the voltage limitcircuit 47 is such that the correct run reference voltage is provided bythe run-bus 42, and this is not necessarily determined by the runexciter generator 48 voltage, depending upon the thread-speed selected,which in turn determines the thread exciter voltage provided by thegenerator 44. The voltage supplied by the run exciter generator 48 willhave to cover a wide range of voltages to provide the desired runreference as a correct steady state value.

If the mill operator wants to deliver the next Workpiece schedule at3,200 feet per minute and he wants -to thread at 1,600 feet per minute,he first sets his preset rheostat 51 for the last stand 20 at 3,200 feetper minute. He can also set the other stands at the correct run-speed inaccordance with the speed cone curve shown in FIG. 3. As soon as thetailend of the last bar of the present schedule leaves the rolling mill,the operator can cause all of. the motor operated rheostats of therespective stands to change to their new desired positions for thesucceeding schedule. However, the mill stands will have decelerated tothread-speed when the previous workpiece strip or bar left thesucceeding stands. This means that the stands are all at thepredetermined thread-speed but are running at approximately the correctspeed ratios for the schedule selected. The operator now adjusts therheostat 81 operative with the thread ramp generator 80 to obtain thecorrect thread-speed out of the last stand 20 by observing the speedindicator for that stand. The adjustment of rheostat 81 will cause allstands to change speed by the same percentage. If desired, the rheostat81 can also have a preset feature such as do vthe mill stands. As soonas the speed of the last stand is correct the mill can then be threaded.It will also be possible to change thread-speed of the mill after a barhas started through the mill provided the rate of change of speed isslow.

the

The mill will then run at ...e 1,600 feet per minute until the stripenters the down coiler or strip winding device 24, which will cause themill to be accelerated to the run-speed by the contactors correspondingto the contactor 58 being closed for each of the stands and thecontactors connected to the thread-bus 40 corresponding to the contactor52 being opened. The run exciter voltage is then raised until thedesired reference value is provided for the run-bus 42. This referencevoltage will have been determined in advance and the mill will have beenset up for this value such that the speed range of the individual standis correct for the involved particular motor design. When the run-busvoltage reaches this value, the limit circuit 4*.-7 will function toprevent the run exciter voltage from being raised further.

In the same manner, any delivery run-speed within the speed cone of themill can be set and also any threadspeed within the range the mill wasoriginally designed for can be set. The thread control is set so thatthe thread voltage can be lowered to a predetermined minimum value andthe run reference can be raised to a predetermined maximum value. Thisallows the necessary flexibility for the mill operator and at the sametime offers a maximum of protection preventing the operator fromattempting to overspeed the stand motors.

in the operation of the apparatus shown in FIG. 4 the strip windingdevice 24 is controlled from the same thread-bus d!) and run-bus 42 asare the stands of the rolling mill. The previous practice was to controlthe strip winding device 24- speed from a pilot generator operative withthe last stand of the rolling mill. This was suitable for rolling millsrun at a substantially constant speed for a given schedule. Thethread-speed of the strip winding device 24 is limited by the top speedat which the workpiece strip can enter the strip winding device 24 ordown coller. When the tail-end of a given workpiece strip leaves theindividual stands of the rolling mill, those stands are individuallyreset to thread-speed to accept the next succeeding bar. However, itmight take in the order of fifteen seconds for the tail-end of apreceding strip to reach the strip winding device 24 after leaving thelast stand 2i). It will not be desirable to attempt to slow down thestrip winding device 2d during the resetting of the mill stand as thismay adversely affect the wrapping of the coil. Since the head end of agiven succeeding workpiece strip may be only a few seconds behind thetail-end of the previous workpiece strip, the stands must be reset tothread-speed immediately after the tail-end leaves. Therefore, it is notpractical to use a pilot generator on the last mill stand 2@ as a speedreference to the down coilers. A load relay can be used to maintain theoperative speed of the motor 7@ until 'the coil is completed, and whenthe strip winding device is not under load it can change its operativespeed to a predetermined thread speed provided by the thread-bus di). ita plurality of alternative strip winding devices or down coilers areprovided, the one which is actually winding strip should be maintainedat run-speed and the other down coilers may change to thread-speed asprovided by the thread-bus 40. ln this same manner only the stripwinding device which is operative with a work strip should follow themill as it increases speed from the thread-speed to the run-speed.Suitable interlocking of the provided selector switch can be provided toaccomplish this function.

Although the present invention has been described with a certain degreeof particularity, it should be understood that the present disclosurehas been made only by way of example and that numerous changes in thedetails of construction and the combination and arrangement of parts maybe resorted to Without departing from the scope and spirit of thepresent invention.

i claim as my invention:

1. In apparatus for contro-lling the operating speed of at `least thedrive motor 'for one stand of a strip rolling mill operative with lastrip coil winding device, the com-v bination of first voltage meansconnected to energize said one drive moto-r to operate at a firstpredetermined speed, second voltage means for energizing said one drivemotor to operate at 'a second predetermined speed greater than said`first speed, load sensing meians operative with said strip rolling millfor providing a iirst control signal when the iWork-piece ystrip enterssaid `strip winding device ,and for providing ya second control signalwhen the workpiece strip leaves said one stand, `and circuit connectionmeans provided between the second voltage means and said one drive motorfor connecting the second voltage means to energize said lone drivemotor from the second voltage means in response to said rst controlsignal and for disconnecting the second voltage means to deenergize saidone drive motor relative to the second voltage means in response to saidsecond control signal.

2. In `apparatus ifor controlling the operating speed of a plurality ofdrive motors for the respective stands ozf a workpiece strip rollingmill operative with a workpiece strip coil winding device, thecombination of lirst voltage means connected to energize simultaneouslyeach of said drive motors to operate at a predetermined threading speed,second voltage means for energizing simultaneously each of said drivemotors to operate :at -a predetermined running speed lgreater than saidthreading speed, load sensing means operative Witlh said strip IWinding[device for providing a first control signal when the workpiece stripybecomes operative with said strip winding device land for providing asecond control signal each time the work-piece strip successively leavesone of said respective stands, and circuit connection means providedbetween the second voltage means and said plurality of drive motors forconnecting the second voltage means fro energize each of said drivemot-ors in response to said iirst control signal such that each drivemotor of the rolling mill simultaneously increases its speed ofoperation from the threading speed to the running speed when `theworkpiece strip becomes operative with said strip winding device 'andfor disconnecting the second voltage means relative to each successivedrive motor in response to each :respective second control signal as thefworkpiece strip successively leave the respective stands ofthe rollingmill.

3. In apparatus for controlling the operating speed of a plurality ofdrive motors of la multiple stand workpiece strip rolling mill operative'with ia strip coil winding device, the combination of lirst voltagesupply means for energizing said drive motors to operate at a firstpredetermined threading speed, second voltage supply means forenergizing said drive motors to operate :at ia second predeterminedrunning speed greater than said iirst speed, first load sensing meansIoperative with said workpiece strip for providing a lirst controlsignal when there occurs a predetermined positioning of the workpiecestrip, circuit connection means provided between the second voltagesupply means and said drive motors for connecting the second voltagesupply means to energize said drive motors in response to said firstcontrol signal, and second load sensing means operative with each one ofsaid multiple stands for providing `a second -controi signal when theworkpiece strip leaves each said one stand, with said ycircuitconnection means being responsive to each said second control signal fordisconnecting the second voltage supply means from the drive motoroperative with each said one stand after the workpiece strip has leftthat respective one stand.

4. In speed control apparatus for la plurality of drive motors operativerespectively with the plurality of stands of a workpiece strip rollingmill including a strip fcoiling device, the combi-nation of firstvoltage supply means for providing a first predetermined speed ofoperation, second voltage supply means for providing :a secondpredetermined speed of operation greater than said iirst speed, firstload .sensing means opera-tive with said strip coiling device forproviding a first output control signal when a workpiece strip is :beingcoiled by said strip coiling device, second floa-d sensing meansoperative |with each of said stands for providing a second outputcontrol signal in accordance with the successive operation of eachrespective stand with the workpiece strip, rst -circuit means responsiveto said rst output control signal and connected between the first andsecond voltage supply means and said drive motors for energizing saiddrive motors to operate at said first speed when a workpiece strip isnot being coiled by said strip ooiling device and to operate ,at saidsecond speed when a workpiece strip is being coiled Iby said stripcoiling device, and second circuit means responsive successively to cachsecond output control signal and connected between the second voltagesupply means and the drive motor for each of said stands tor controllingthe energizlation of the respective drive motors Eby the second voltagesupply means in accordance with the successive operation of saidplurality tot stands with .the workpiece strip.

5. In speed control apparatus for a plurality of drive motorsrespectively operative with the multiple stands of a workpiece striprolling mil-1 including Ia strip coiling device, the combina-tion of rstvoltage supply means operative with said motors to provide a firstpredetermined speed `off operation, second voltage supply meansoperative with said motors to provide a second predetermined spced ofoperation greater than said first speed, first xload sensing meansoperative with said strip coiling device yfor providing a first outputcontrol signal when the leading-end of the work-piece strip is beingcoiled by said strip coiling device, second Iload sensing meansoperative rwith each of said stands to sense the passage of the tail-endof the workpiece strip through each of said stands, first circuit meansconnected between 4the first voltrage supply means and said drive motorsfor initially energizing a'll of said motors to opera-te at said firstspeed, second circuit means connected between the second voltage supplymeans and all of said drive motors and being responsive to said `iirstoutput control signal lfor energizing said motors -to operate at saidsecond speed when a Workpiece strip is 'being coiled by said stripooiling device, and third circuit means operative with the second lloadsensing means :and operative with the second volt-age supply means forsequentially returning each o said motors to operati-on at said iirstspeed las the tail-end of the workpiece strip Irespectively leaves eachof said stands in passing through said workpiece strip rolling mill.

References Cited by the Examiner UNITED STATES PATENTS 2,342,767 2/44Stoltz 80-351 3,109,330 11/63 Barnitz et al 80-35.1

FOREIGN PATENTS 214,663 4/58 Australia.

CHARLES W. LANHAM, Primary Examiner.

W'IILLIAM J. STEPHENSON, Examiner.

5. IN SPEED CONTROL APPARATUS FOR A PLURALITY OF DRIVE MOTORSRESPECTIVELY OPERATIVE WITH THE MULTIPLE STANDS OF A WORKPIECE STRIPROLLING MILL INCLUDING A STRIP COILING DEVICE, THE COMBINATION OF FIRSTVOLTAGE SUPPLY MEANS OPERATIVE WITH SAID MOTORS TO PROVIDE A FIRSTPREDETERMINED SPEED OF OPERATION, SECOND VOLTAGE SUPPLY MEANS OPERATIVEWITH SAID MOTORS TO PROVIDE A SECOND PREDETERMINED SPEED OF OPERATIONGREATER THAN SAID FIRST SPEED, FIRST LOAD SENSING MEANS OPERATIVE WITHSAID STRIP COILING DEVICE FOR PROVIDING A FIRST OUTPUT CONTROL SIGNALWHEN THE LEADING-END OF THE WORKPIECE STRIP IS BEING COILED BY SAIDSTRIP COILING DEVICE, SECOND LOAD SENSING MEANS OPERATIVE WITH EACH OFSAID STANDS TO SENSE THE PASSAGE OF THE TAIL END OF THE WORKPIECE STRIPTHROUGH EACH OF SAID STANDS, FIRST CIRCUIT MEANS CONNECTED BETWEEN THEFIRST VOLTAGE SUPPLY MEANS AND SAID DRIVE MOTORS FOR INITIALLYENERGIZING ALL OF SAID MOTORS TO OPERATE AT SAID FIRST SPEED, SECONDCIRCUIT MEANS CONNECTED BETWEEN THE SECOND VOLTAGE SUPPLYMEANS AND ALLOF SAID DRIVE MOTORS AND BEING RESPONSIVE TO SAID FIRST OUTPUT CONTROLSIGNAL FOR ENERGIZING SAID MOTORS TO OPERATE AT SAID SECOND SPEED WHEN AWORKPIECE STRIP IS BEING COILED BY SAID STRIP COILING DEVICE, AND THIRDCIRCUIT MEANS OPERATIVE WITH THE SECOND VOLTAGE SUPPLY MEANS ANDOPERATIVE WITH THE SECOND VOLTAGE SUPPLY MEANS FOR SEQUENTIALLYRETURNING EACH OF SAID MOTORS TO OPERATION AT SAID FIRST SPEED AS THETAIL-END OF THE WORKPIECE STRIP RESPECTIVELY LEAVES EACH OF SAID STANDSIN PASSING THROUGH SAID WORKPIECE STRIP ROLLING MILL.